To draw a line parallel to a given line (fig. 3-6, view A), adjust the hypotenuse of a triangle in combination with a straightedge (T square or triangle) to the given line; then, holding the straightedge firmly in position, slip the triangle to the desired position and draw the parallel line along the hypotenuse. To construct a line perpendicular to an existing line, use the triangle and straightedge in combination, with the hypotenuse of the triangle resting against the upper edge of the straightedge (fig. 3-6, view B). Adjust one leg of the triangle to a given line. Then slide the triangle along the supporting straightedge to the desired position and draw the line along the leg, perpendicular to the

Figure 3-6.-Drawing parallel and perpendicular lines.

leg that was adjusted to the given line. In the same manner, angles with multiples of 15 degrees may be drawn, using the triangle combinations shown in figure 3-4.

Many drawings that you will prepare require the construct ion of various curved lines. Basically there are two types of curved lines: circles and segments of circles, called arcs, which are drawn with a compass; and noncircular curves, which are usually drawn with french curves. In this chapter we will discuss only techniques for using the compass and the french curve. Application of compass techniques in geometric construction will be covered in chapter 4.